Figure 1. Fission track grain age versus (A) Dpar (etch figure size) and (B) Cl content in atoms per formula unit. (A) Age populations overlap with respect to Dpar; age groupings (number of grains in brackets) are arbitrary and based on sorting grain ages. Intermediate ages could belong to either the younger or older population. (B) Two age populations are separated at 0.125 apfu Cl; younger high Cl grains may be caved from the Cretaceous. Pooled ages (± one standard devitaion) are shown along with _X² probabilities (Q).